1. Field of the Invention
This invention relates to methods of distinguishing the source of water found in subterranean formations where oil and gas wells are drilled, and in particular to determining deuterium oxide concentrations in such formations.
2. Background Art
The use of so-called “tracers” in a variety of applications is well-known. “Tracers” represent a variety of chemical compounds that, under the conditions of use, act or react in a predictable way such that their presence, absence or activity in a particular location may be detected. This detection is useful in ascertaining and/or measuring events occurring at that location, i.e., in obtaining information about a particular microcosm such as, for example, a particular formation region at a drillsite.
Tracers that have traditionally been used in oil and gas drilling applications include, for example, salts of various types, such as potassium chloride. These materials operate to “tag”, i.e., act as a tracer in, steam, oil, gas or water which is introduced into the subterranean formation or well-bore using any of a wide variety of known equipment and methods.
One application for tracers has been to track and quantify subterranean water migration, and in particular to track and quantify the infiltration of formations by drilling fluids. For example, it is known that, depending upon formation pressures, porosity and other variables, formations may be contaminated by significant amounts of drilling fluids. However, because this invasion may affect the accuracy of certain calculations and calibrations relating to oil and gas well preparation and production therefrom, it is desirable to be able to distinguish the effects of the infiltration from inherent formation characteristics.
This problem is particularly apparent when water-based drilling fluids are used in a formation that, itself, includes water. While known applications of certain tracers may confirm drilling fluid contamination of the formation, they generally cannot distinguish between the sources of the water in which they are carried. Because they may not distinguish the water source, calculations based on their presence in formation samples will not be entirely accurate. Because the calculations are essentially inaccurate, calibrations and other determinations based upon such calculations will have a margin of error. This margin of error may lead to non-optimal and even poor decisions relating to well management and production.
Thus, what is needed in the art is an improved method of ascertaining and measuring the infiltration of water-based drilling fluids into a subterranean formation, such that the source or sources of water in the formation may be distinguished.